When you maximize an application, Instant Text requests that the application takes the whole screen minus the space needed for Instant Text. Some applications refuse to do so - Chrome is a famous example - and take the whole screen, resulting in Instant Text being underneath.
Our recommendation is to NOT maximize such applications, but resize them manually so that they take most of the screen, but leave the space needed for Instant Text.
Another possibility is to put Instant Text always on top (Options->Elements->Check Always on Top), in which case you will see Instant Text. The drawback is that in this case Instant Text hides the bottom of the maximized client that does not want to share the screen real estate.